1. Field of the Invention
The present invention relates to a method and an apparatus for displaying a translucent object, and more particularly, to a method and an apparatus suitable for realistic displaying an object which is not perfectly opaque and which has a fairly low transparency such as frosted glass, paper and the like, by a graphics display apparatus.
2. Description of Related Art
In conventional graphics systems for displaying images of objects, improvements in function are directed to the realistic display of various objects. A display with superior quantitative and qualitative affects can be obtained by selecting whether to display an object surface as an opaque surface or as a translucent surface, corresponding to the type of object.
To be more specific, when a translucent object is displayed in a surface model representation, the object is first defined as a translucent object, then the actual display color is determined by mixing the color of the object and the color of background, based upon the transmissivity of the translucent object. Consequently, when a light source is seen through a translucent object, the light source is displayed with decreased intensity corresponding to the transmissivity of the translucent object, and in color corresponding to the color of the translucent object.
When displaying a translucent object as above-mentioned, a translucent object having high transparency such as cellophane or the like can be displayed realistically. However, a translucent object having a low transparency such as frosted glass or the like is displayed rather different from its actual appearance. That is, the representation of a translucent object having a low transmissivity can be performed by decreasing the mixing rate of light from the light source, but the representation of a translucent surface having a low transparency cannot be performed realistically because the outline of the light source is distinctly displayed as in the case of cellophane or the like. To overcome the disadvantage, modelling of a blurred background such as seen through the translucent object having a low transparency is needed. However, the modelling is not actually performed, and only imperfect displaying of the translucent object is accordingly performed.
When an object to be displayed is paper for example, the object to be displayed is generally defined as an opaque object. However, paper selectively becomes an opaque object or a translucent object, depending upon the relative position of the paper with respect to a viewpoint and a light source. The paper is displayed fairly differently from its actual appearance accordingly. In particular, when a model such as a paper cup is displayed, an opaque portion and a translucent portion are seen, and both portions vary depending upon the relative position of the paper cup to the viewpoint and the light source. A realistic visual display hardly can be obtained accordingly.